DCI Jill Marsden is a fictional character in the BBC soap opera EastEnders, played by Sophie Stanton. She made her first appearance on 5 March 2001 investigating the shooting of Phil Mitchell (Steve McFadden), which was part of the whodunit storyline "Who Shot Phil?". Marsden returned in 2002, 2003 and 2009 (for another whodunit storyline, "Who Killed Archie?"). She returned on 5 January 2012 for her third whodunit storyline, "Who's Stalking Phil?", departing four months later on 10 May 2012. Marsden returned for two episodes on 17 August 2012 to conclude the latter storyline. On 16 July 2015, she returned for part of the "Who Killed Lucy Beale?" whodunit storyline.

When she was brought back in 2009, Marsden's feelings were explored in a segment of the BBC EastEnders homepage entitled "Marsden's Video Diaries", documenting the character's thoughts about the storyline in which she was involved. Marsden's relationship with Phil has been explored since her first appearance, with the BBC describing their relationship as a "romance in negative...her ultimate dream is that some day she'll get [Phil] behind bars" and the Daily Mirror Tony Stewart calling her Phil's "arch enemy".

The character has been criticised by police detectives who felt that Marsden's habit of discussing investigation details with suspects (as her colleagues accepted bribes) did not properly represent their profession. In response, the BBC said it had sought advice from a police consultant for storylines involving Marsden.

Development Characterisation Nicknamed the "female sleuth" by the Daily Record, Marsden's profile on the EastEnders website describes her as "fearless, [a] no-nonsense copper and the scourge of Walford’s criminal fraternity." The East Anglian Daily Times described Marsden as "tough", Ian Hyland from The Mirror called her "scary" and Nancy Banks-Smith from The Guardian characterised her as "strict". Naomi Mcelroy described Marsden as a "curly-haired copper", but said as a detective she was "rubbish"; Polly Hudson from The Daily Mirror similarly opined, saying she was "useless" (as did Mcelroy), and stated that Marsden was "making a right pig's ear" of investigating Archie's (Lamb) murder. The Daily Mirror Tony Stewart characterised her as "vindictive".

Introduction, 2002 and 2003 returns Marsden first appeared on 5 March 2001 in the "Who Shot Phil?" storyline. In the whodunit storyline the five main suspects were Dan Sullivan, Steve Owen, Lisa Shaw, Ian Beale and Mark Fowler. A source in the Daily Record said, "Sooner or later the truth will out. But until then there's going to be a lot of probing going on." She left on 27 March 2001 after unsuccessfully identifying the shooter (who turned out to be Lisa). In 2002 she appeared in January, April and from 14 November to 6 December. In November, when Marsden returns, the police suspect that Phil has murdered his ex-wife Lisa. The Daily Mirror said, "They are the words Phil Mitchell has heard many times before. 'You're nicked', baldy. Intrepid DCI Marsden may not be a Jane Tennison, but she's nabbed her prime suspect. "I've got some good news for you, Phil," she says, after arresting him on suspicion of murder. "The police in Portugal found your jacket. Unfortunately for you, it's covered in blood. Mrs Fowler's blood..." In 2003, Marsden returned in March July, August, November and for a longer stint in December.

Who Killed Archie? and 2012 returns

In November 2009, it was reported that Stanton would reprise her role as Jill. Digital Spy forum members had previously pointed out that her return was hinted at in a photo on the official EastEnders website and in a feature ("Script Peek") where Phil is quoted as saying, "I know exactly what makes her tick" before adding "I've wriggled off her hook so many times. She's already picturing me standing in the dock" in the 29 December episode. Marsden returned to investigate the murder of Archie Mitchell. A source told Digital Spy, "Marsden has a score to settle with Phil. She was never far behind Phil when he put a foot out of place all those years ago and she's back with a vengeance...With so many people in the frame for Archie's murder, Marsden has a difficult job on her hands if she wants to pin it on Phil." Of her return she said, "It came completely out of the blue, and knocked me for six."...I really thought Marsden was no more. It was a really great surprise because I'd just finished a year's run at the National Theatre, appearing in a new play called England People Very Nice – so it couldn't have come at a better time." She returned on 28 December 2009.

Although Stanton did not know who murdered Archie, she guessed that it could be Stacey Slater (which turned out to be correct). Speaking of this, she said that Sophie was one of the few to correctly guess it was Stacey. "I had an epiphany about a week before the live episode. It was a memory of the whole Who Shot Phil? storyline, and how there were eight different suspects, including some really hard blokes, and it turned out to be Lisa. I knew DCI Marsden wasn't going to get the culprit, because of a couple of scenes of the following episode we'd shot in December, and I thought that narratively, Stacey was the only person who the audience would forgive, and who could get away with it. That was my theory and it turned out to be right!" Naomi Mcelroy from The Sunday Mirror thought that Marsden could be Archie's killer. Marsden left on 22 February 2010, and returned on 5 January 2012. She returned after Phil is framed for Kevin Wicks' (Phil Daniels)'s death and that of a homeless man, who died accidentally in a car-lot fire (part of an insurance scam). According to Inside Soap the police would begin questioning Phil's former fiancée Stella Crawford's death, teasing Marsden's return: "The investigation is set to bring Phil face to face with his old nemesis, DCI Marsden – and this time she'll stop at nothing to put the bad boy permanently behind bars". Digital Spy reported that Marsden re-opens the investigation into Stella's death, "suspecting that all is not what it seems". Finally, Marsden returned for two single episodes on 17 August 2012.

Who Killed Lucy Beale? In July 2015, it was revealed that Stanton would be reprising her role as Marsden for the continuation of the Who Killed Lucy Beale? storyline. Whilst viewers know Bobby Beale (Eliot Carrington) is the culprit, Marsden, Samantha Keeble (Alison Newman) and Cameron Bryant (Glen Wallace) will reportedly make an arrest for the murder, arresting an innocent suspect.

Storylines 2001–2003

Jill Marsden first appears on Albert Square in March 2001, having been assigned as the chief police detective in charge of investigating the shooting of local hardman Phil Mitchell (Steve McFadden). She identifies the five main suspects: Phil's stepson Ian Beale (Adam Woodyatt), ex-business partner Dan Sullivan (Craig Fairbrass), sworn enemy Steve Owen (Martin Kemp), love rival Mark Fowler (Todd Carty), and former girlfriend Lisa Shaw (Lucy Benjamin). After Marsden interrogates each of the suspects behind Phil's shooting, it is eventually transpired in April 2001 that Lisa was the culprit. However, Phil gradually forgives Lisa and decides to frame Dan for the crime instead. He plants the gun, which Lisa took from Steve's office, in Dan's possession and enables for Marsden and her colleagues to arrest Dan for shooting Phil. A couple of months later, however, Dan is acquitted due to lack of evidence. Marsden later arrests local housewife Little Mo Slater (Kacey Ainsworth) for the attempted murder of her husband Trevor Morgan (Alex Ferns). Little Mo claims self-defence, since she has been a victim of domestic violence at the hands of Trevor. The trial ends, with Trevor's treatment of Little Mo revealed. In 2003, local resident Sonia Jackson (Natalie Cassidy) visits Marsden with evidence that Phil killed his ex-girlfriend Lisa. Marsden sets up a honey-trap for Phil in order to obtain a confession from him, with PC Kate Morton (Jill Halfpenny) and DI Dominic Price (Paul Brennen) aiding her in the case; however, this fails when Kate falls in love with Phil and Marsden fires her. Marsden arrests Phil, but with insufficient evidence and no confession he is released. It later emerges that Lisa is safe and well, and Phil is innocent. This forces Marsden to let Phil off the hook, but she later arrests him for armed robbery; Phil's arch-rivals Den Watts (Leslie Grantham) and his illegitimate son Dennis Rickman (Nigel Harman) have worked together to set him up for the crime in revenge for what he did to their beloved family member, Sharon (Letitia Dean).

2009–2010

Marsden reappears on Albert Square in 2009 when Phil's villainous uncle, Archie (Larry Lamb), is murdered on Christmas Day 2009. She arrives on the scene when several people claim that Archie's partner-in-crime, Janine Butcher (Charlie Brooks), had killed him - though but Marsden waits before questioning her, and decides to interrogate the Mitchells first. She makes a televised appeal for witnesses and later interviews Phil, but he is provided an alibi by his new girlfriend Shirley Carter (Linda Henry). A few days later, a red fingernail is found at the scene of the murder; Marsden visits the female locals, checking their hands. When Marsden notices Shirley's best-friend Heather Trott (Cheryl Fergison) is at a vulnerable state over the matter, she questions Heather about Christmas Day and Heather accidentally tells Marsden that Phil wasn't there. Marsden interviews Phil and later visits his home, asking to see the clothes he was wearing on Christmas Day. Shirley shows her a clean shirt; Marsden closes the laundrette, hoping anyone with blood-stained clothes will not be able to wash them. After a tip-off, Marsden arrests Phil's sister Sam (Danniella Westbrook) for the murder; Sam has accused her and Phil's mother, Peggy (Barbara Windsor), for killing Archie. Later on, Marsden confirms that she was there to talk to Peggy; she had been questioning Peggy and Sam at the police station. Peggy is released without charge; however, Sam is detained for jumping bail. Marsden visits Janine, who insists that people will say anything to get her in trouble. She asks Janine why she was out in the cold on Christmas Day, and asks if Janine knows where Archie's laptop as it had gone missing.

On 18 January, Marsden arrests Ian after Janine told her that Ian took advantage of her, stole Archie's laptop, which had a recording of them having sex on it, and dumped it in the canal. Ian refuses to talk, but when Marsden shows him CCTV footage of him dumping the laptop, and then shows him the recovered laptop, he admits visiting Archie on Christmas Day; claiming that Archie was threatening him and that he merely visited him to delete the recording. Ian denies murdering Archie, but Marsden is unconvinced and later charges him. A couple of days later, Janine tells Marsden she saw Ian leave the Queen Victoria on Christmas Day but the bust of Queen Victoria was on the bar after he left. Marsden places Janine at the scene, but she also denies murdering Archie. Marsden tells Ian that although the murder charge will be dropped, he will still be charged with burglary and theft of Archie's laptop. She and DC Wayne Hughes (Jamie Treacher) attend Archie's funeral, watching people's reactions in the hope of a new lead. Peggy returns to Archie's grave; when Marsden asks why, she explains that she didn't believe him when he said his cancer had returned.