The family of the suspect in the Finsbury Park mosque attack has claimed he had mental health problems and recently tried unsuccessfully to get himself sectioned.

Darren Osborne’s sister, Nicola, claimed he was on antidepressants and had thrown himself into a river in the last couple of months. She insisted he was neither a racist nor a terrorist.

It is understood that health officials in Cardiff, where Osborne lived, are working with police investigating the Finsbury Park attack to help establish the suspect’s mental state.

Police have been granted a warrant to hold Osborne until the early hours of Saturday following the incident on Monday in which a van was driven into a crowd of worshippers. One person died and 11 were injured.

Osborne, 47, is under arrest on suspicion of the commission, preparation or instigation of terrorism, including murder and attempted murder.

A picture has emerged of a deeply troubled, unstable man. Osborne had a partner and four children, but though he saw the youngsters regularly he did not appear to be staying at the family home and is said to have slept rough sometimes in a tent or in vehicles.

On the Saturday evening before he drove to London he was thrown out of the Hollybush pub in Cardiff after angrily talking about a pro-Palestinian march in London. Over the weekend he was heard calling his Muslim next door neighbour’s son “in-bred”.

Police were called in the early hours of Sunday to a report that Osborne was sleeping in the van allegedly used in the attack, but did not take any action after deciding no offence had been committed.

There is no immediate evidence that Osborne was an active member of a far-right organisation. He does, however, appear to have a Twitter account, which he has never used to send his own tweets, but he instead followed 32 other users, including Paul Golding and Jayda Fransen, the leaders of the far-right party Britain First.

Speaking outside her flat in Weston-super-Mare, Somerset, Nicola Osborne, 50, said her brother was mentally frail. She told the Daily Mirror: “He tried to kill himself six, eight weeks ago. He threw himself into the river in Cardiff. He asked to be taken into care, to be sectioned, but they wouldn’t do it.

“He was on antidepressants. He came to see me after he tried to kill himself. He showed me the bump on his head.”

Osborne grew up in Weston-super-Mare and has been described as a troublemaker by family friends and neighbours there.

Nicola Osborne said: “He asked me if he could stay, but he has made my life a misery over the years. Everyone knows Darren. I’ve lost jobs, boyfriends after people found out I am Darren Osborne’s sister.”

Police are using CCTV cameras and automatic numberplate recognition technology to track Osborne’s movements from Cardiff to London.

One line of inquiry will be whether he drove anywhere near the al-Quds Day march, which took place in Westminster on Sunday afternoon and is often targeted by far-right activists.

South Wales police have confirmed that officers were called out to the north Cardiff suburb of Pentwyn at 12.27am on Sunday after a neighbour reported a man, believed to be Osborne, was sleeping in a van and appeared to have been drinking heavily.

A police spokesman said: “Officers attended, a male was asleep inside the vehicle, which showed no signs of having been driven recently. The officers’ assessment was that no offences were disclosed.”

It is believed Osborne hired the van several days before and parked it in a street close to his family home in Pentwyn. Neighbours saw him making phone calls from the van late at night.

According to witnesses at Finsbury Park, Osborne shouted: “I want to kill all Muslims” as he drove a van into a crowd of worshippers in the early hours of Monday morning.

Camera phone footage showed him being captured by worshippers, who attacked him as he screamed “kill me”. When he was eventually arrested and loaded into the back of a police van in handcuffs, he gestured to the crowd.

The Cardiff and Vale health board refused to discuss whether Osborne had tried to get himself sectioned.

A spokesperson said: “In line with public protection, the health board works closely with police colleagues … and is unable to comment on the health needs of individual members of the public.”