Serial killer Joanna Dennehy is believed to have tried to kill herself in jail after apparently making a grisly suicide pact with her prison girlfriend.

Dennehy, 35, is understood to have been found with her throat slit, while her lover had cut her wrists.

A source told The Sun: “When the guards found them they were entwined on the floor, which was covered in blood.”

“They think they need splitting up now to make sure it doesn’t happen again.”

The pair were rushed to the hospital, where their injuries were treated.

They were then returned to HMP Bronzefield prison in Surrey, England.

But once back inside, Dennehy launched a second suicide attempt — which again failed.

She is now believed to be being cared for by medics.

A prison spokesman said he could not comment on individual prisoners.

Dennehy is one of only two female prisoners serving a life sentence in the UK.

She stabbed three men to death over a 10-day period in March 2013, before knifing two others.

Branded “pure evil” by criminology experts, Dennehy said she committed the murders because it was “moreish and fun.” (“Moreish” is British slang for an agreeable experience that you want more of.)

Her victims’ bodies were found in ditches.

The first was Lukasz Slaboszewski, 31, a Polish national whom she had met a few days earlier.

She convinced him to meet up, implying that they would have sex.

Instead, she stabbed him in the heart and dumped his body. The following week, 56-year-old Falklands war veteran John Chapman was knifed to death by Dennehy.

Later that day, she murdered her landlord and lover Kevin Lee, 48.

His body — dressed in a black sequin dress — was found the following day with stab wounds in the neck and chest.

It was reported that Dennehy had wanted to kill nine men in total, to be like killers Bonnie and Clyde.

She was caught two days after going on the run when police launched a triple murder probe.

In court, Justice Spencer told her: “Although you pleaded guilty, you’ve made it quite clear you have no remorse.”

“You are a cruel, calculating, selfish and manipulative serial killer.”

The Sun revealed last year that Dennehy has bragged she had killed a fourth person.

She said this victim was also a man, but at the time the Ministry of Justice said they had found “no evidence” to support her boasts.