Cleveland Police are appealing for information after a man died just minutes after he walked into a police station.
At 9.30pm on Wednesday, 50-year-old Laurence French entered Middlesbrough Police Station.
Whilst speaking to staff he became seriously ill and collapsed on the floor.
Despite the efforts of staff, police officers and ambulance staff, he was pronounced dead a short time later at James Cook University Hospital.
A post mortem examination was carried out yesterday evening, however, those findings are not being released at this stage for operational reasons.
The police believe that Mr French may have been burgled at his home address in Alwent Road, Middlesbrough, prior to attending the police office.
Officers are investigating the circumstances leading to his death and whether his death is linked to the burglary.
Mr French is believed to have been vulnerable and may have been targeted due to his vulnerability.
Last night, three males aged 39, 40 and 42 were arrested on suspicion of murder and aggravated burglary.
This morning a fourth man, aged 66, was arrested on suspicion of handling stolen goods. All remain in custody today.
A number of house searches are ongoing in the Middlesbrough area this morning in connection with the incident.
Police are appealing to anyone who knew Mr French to contact them and to anyone who was in the area of Alwent Road on Wednesday evening, or anyone who may have seen or spoken to him that day, to get in touch.
Officers are also urging anyone who knows anything about a potential burglary at his home or those who may be responsible to contact them on the non-emergency number 101, or alternatively, contact Crimestoppers anonymously on 0800 555 111 or www.crimestoppers-uk.org.