In John Hinckley Jr's mind it was love.

He would look at her often and write her letters, he had an aching to be near her.

He thought she wanted him too, but he was nothing but delusional.

The woman he was pining after was Hollywood actress Jodie Foster, and she did not know he existed until he stalked her and even attempted to assassinate former US President Ronald Reagan in 1981 to impress her.

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Secret Service agents and bystanders attend to those injured in the assassination attempt on Ronald Reagan by John Hinckley. Photo / Getty Images
Secret Service agents and bystanders attend to those injured in the assassination attempt on Ronald Reagan by John Hinckley. Photo / Getty Images

He was found not guilty for the assassination attempt and was instead declared insane and sent to a psychiatric hospital where he had to deal with his mental illness - Erotomania.

It's been more than 35 years since the attempted assassination and the 61-year-old has now been released from the mental hospital in Washington DC.

Erotomania is a rare delusional syndrome and according to the Journal of the National Medical Association, it involves people who believe somebody with a higher social, political or economic status is in love with them.

While Erotomania, also known as De Clerambault's syndrome, is uncommon, there have been a number of celebrities at risk. One man even became so obsessed with superstar Justin Bieber he planned to kill him.

Prison inmate Dana Martin hatched a plan in 2012 to murder Bieber after he felt rejected by him.

Martin, a convicted killer, became obsessed with Bieber after hearing his songs and even got a tattoo of him on his leg and wrote him a number of letters the popstar never responded to.

Enraged by the rejection, Martin hatched a plan to kill, and recruited two men to castrate and murder Bieber during a concert in New York. The plot was foiled when Martin told police.

One man even became so obsessed with superstar Justin Bieber he planned to kill him. Photo / AP
One man even became so obsessed with superstar Justin Bieber he planned to kill him. Photo / AP

There were also two cases of Erotomania followed by researchers for more than 30 years to learn more about the rare condition.

In 1971, a well-dressed woman who appeared to have no psychotic delusions began presenting with a strange illness.

She talked about a man who she believed would become her boyfriend, even though they had never gone on a date and she watched him afar in class.

She said she knew he loved her and she was attracted to him because of his strong feelings towards her.

According to the Journal of the National Medical Association, she believed this man was empty without her and was chasing after her, but classmates, family, friends and neighbours were getting in the way and plotting to destroy their relationship.

She believed he was sending her messages of love and she would see them on licence plates and believed whenever she saw the colour purple, it was a message from him.

She claimed even the US President was aware of their love for each other and her delusions persisted for up to four years.

She began to develop other delusions and according to the Journal of the National Medical Association, she claimed he visited her at night, married her and even got her pregnant.

She believed she had given birth to a number of children but they had been taken away from her.

Another woman, described as very attractive, fell in love with her professor at her art college.

He was married but she thought he was in love with her and she refused to accept his marriage.

The Journal of the National Medical Association said she would send him letters, cards and flowers and would attempt to enter his home. She believed he was pretending to be married and secretly loved her.

John Hinckley, accused assassinate of President Reagan, sits in the back of this motioned vehicle outside the federal court in DC. Photo / Getty Images
John Hinckley, accused assassinate of President Reagan, sits in the back of this motioned vehicle outside the federal court in DC. Photo / Getty Images

Her delusions continued for years and the professor took her to court and she was followed by a psychiatrist employed by a psychiatric hospital where she had previously been admitted.

Like the first case, she also thought people were plotting to keep her and the professor apart and even thought they wanted to kill her.

The woman began having delusions about 1965, and 30 years later, she still believed they were in love.

The man however said he was not interested in her and wished she didn't become a part of his life in such a forthcoming way.

It is believed she still continued to have fantasies about him, even though psychiatrists told her he was not interested. According to the Journal of the National Medical Association, Erotomania is a misunderstood disorder but patients can bring chaos into the lives of their phantom lovers.

"A grotesque drama often ensues when erotomanic patients act on their delusions, relentlessly bombarding their victims with telephone calls, letters, gifts and visits," the journal said.

"Persistent surveillance and stalking may occur. After repeated professions of love and advances are unrequited, these patients may become dangerous, as resentment and rage are mobilised in response to perceived rejection by the love object."

In Mr Hinckley's case, he became obsessed with Foster after watching Taxi Driver, where the main character plans to assassinate a presidential candidate.

In a bid to get Foster's attention, he attempted to assassinate Reagan.

In a letter addressed to the actress before the failed assassination, dated March 30, 1981, he expressed his feelings.

Letter from John Hinckley to Jodie Foster. Photo / Getty Images
Letter from John Hinckley to Jodie Foster. Photo / Getty Images

"I will admit to you that the reason I'm going ahead with this attempt now is because I just cannot wait any longer to impress you. I've got to do something now to make you understand, in no uncertain terms, that I am doing this for your sake!" he wrote.

In another letter he said "I love you six trillion times. Don't you like me a little bit?".

Now Mr Hinckley is released, he hopes to "fit in" and become a "good citizen".