A convicted killer who is still at large after absconding from the John Howard secure mental health unit in Hackney could have been helped to escape by a man who worked there.

Lerone Michael Boye – who murdered a teenager two years ago – absconded from the John Howard Centre in Kenworthy Road, Homerton, last Wednesday afternoon.

This morning police charged Dean Ablakwa, 29, who is a member of staff at the John Howard Centre, with conspiracy to assist an offender escape from lawful custody.

Mr Ablakwa, from north London, has been remanded in police custody and will appear at Thames Magistrates’ Court this morning.

Boye is the second potentially dangerous patient to escape from the centre in the space of four months.

Boye was sentenced to 28 years in jail at the Old Bailey last December for the murder of 17-year-old Kelvin Chibueze in August 2011.

The teenager was attacked in a mass brawl involving knives and bar stools at a private party in Ilford.

He managed to flee, but tripped outside a Lidl supermarket and four rival gang members – including Boye – sat on his legs to stop him running away, before stabbing him repeatedly with a foot-long blade.

The decision to place Boye in a medium secure facility – rather than one of the UK’s three high-security hospitals – was made jointly by the Ministry of Justice, the prison service and the East London NHS Foundation Trust.

Security and processes at the John Howard Centre are now being reviewed for the second time in four months, “as a matter of urgency”.

An investigation was carried out after the last patient absconded from the unit in June, the results of which the East London NHS Foundation Trust refused to share with the Gazette, saying it was for internal use and “lessons had been learned”.

The centre is surrounded by a perimeter fence, which is checked daily for any sign of interference or disturbance, and has a double-locked entrance system which is controlled by authorised staff. CCTV cameras are monitored 24 hours a day.

While some patients are allowed leave from a medium secure unit with permission from the Ministry of Justice as part of a rehabilitation programme, those transferred for mental health treatment from a prison are not.

In June 2012 a man escaped from the unit, and was caught by police six days later and sent to prison.

This August James Lisbon – who police warned the public not to approach – failed to return from escorted leave and is still AWOL.

In January 2011 Chidi Njoku, a schizophrenic man with a history of violence gave his support worker the slip while out walking.

He was found within a week – but a year later he ran away again while on leave.

Anyone who sees Boye – who has a horseshoe shaped scar on his cheek, a goatee beard and a gold tooth – is advised to call 999.