Viewers took to social media with anger after they noticed a glaring factual error in Erin Reagan’s murder case.

Although Blue Bloods’ most recent episode saw a clash between Erin Reagan (played by Bridget Moynahan) and her sister-in-law Eddie Janko (Vanessa Ray), fans were left distracted by a major blunder. As a murder case went to court, a knowledgeable fan revealed the show made a huge mistake with the law.

During the season 13 episode, officers Eddie and Luis Badillo (Ian Quinlan) arrived on the scene of a stabbing, where a young girl confessed to the crime.

However, she refused to speak to assistant district attorney Erin, after Eddie advised her not to speak to anyone without a lawyer present.

This sparked a major feud between the two which resulted in a huge confrontation.

Tensions soon escalated after Erin called Erin’s ex-husband Jack Boyle (Peter Hermann) who also happens to be a defence attorney.

While Erin was upset she wasn’t given a heads-up about Jack’s return, fans were taken aback as the case went to court.

Redditor u/Dana07620 took the forum’s fan page to rage at the error stating: “I can’t get past the stupid in Friday’s episode.

“The stupid being, Erin saying that it’s too late now as the knife purchase was tracked after the grand jury declined to indict.”

They insisted: “There is no double jeopardy with grand juries.

“When you’ve got more evidence, you can always re-present it to the grand jury.”

The Redditor explained: “Double jeopardy only applies with the actual trial.

“A grand jury just decides if someone is going to be indicted which leads to them being tried.

“How on earth can the writers not know anything so basic??”

They continued: “For that matter, why even have the grand jury before the evidence is in?

“If the person is not under arrest, there’s no hurry on the grand jury because there’s no clock on charging them.”

Taking to the comments u/kayky97 agreed: “I thought the same thing. My first thought was that she jumped the gun on the grand jury, but even so, she can re-present.”

A confused u/ghostwriter623 echoed: “Yeah, this one was a head-scratcher for me. Why did she tell Anthony to find out where the knife came from and then not wait for the answer?”

The viewer added: “Furthermore, why are she and Anthony handling the investigation? I’m definitely a BB apologist for many things, but this one was just bizarre.”

Despite their history, Jack and Erin went up against each other in court.

Erin was convinced the murder was pre-meditated but as she didn’t have any evidence, her points didn’t hold up in court so Jack won.

However, the future of Eddie and Erin’s friendship remains uncertain, fans will have to tune in next week to see if they will be able to find common ground.