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This series of the popular crime programme is set around the Murder Investigation Team who are looking into the death of the journalist. With a corrupt police officer among them, AC-12 are now investigating the team.
And one fan of the show has made an interesting observation about PC Ryan Pilkington, who has been planted inside the police station by the OCG, and they've shared their theory on Twitter.
Matt Page (@mrmattpage) wrote: "Subtle observation at start of S6E4 #LineOfDuty."
He added the camera turned towards Ryan at the exact moment DI Kate Fleming talks about Vella's murder, as well as when DCI Jo Davidson says the word "burglary".
He Tweeted: "Jo said due to Buckells, leads had been overlooked in the Vella murder. At exact moment she says 'burglary' the camera focuses on Ryan; again when Kate says 'he discharged the fatal shot'. Ryan killed Vella #lod."
And fans are convinced by this theory too.
One fan commented that Ryan seemed "very practiced at murdering when in that lake".
While another referenced the end of the latest episode, when Ryan told DCI Jo Davidson that the cause of death for Jimmy Lakewell was "being a rat, mam," as well as when he held the gun to her head as she entered her flat.
"One of the COLDEST lines this show has ever had to offer," one Twitter user commented. "I'm thinking Ryan killed Vella himself with the way he pointed the gun."
Let's face it, Ryan is shifty and we've known of his involvement with the OCG ever since he was dropping burner phones off on his bike, way back in series one.
So could he have killed Gail Vella?
Only time will tell.
Line of Duty series six continues on Sunday evenings at 9pm on BBC One.
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