An Ottawa senior who spent years in prison after being convicted in the drowning death of his pregnant wife in the 1950s has been charged with arson in relation to two Sunday house fires.

Gaston Nicholas

An archival photo of Gaston Nicholas and his wife, who drowned while on a canoe trip. (CBC)

Gaston Nicholas, 78, was arrested Sunday afternoon after a police pursuit on Highway 417, near Pinecrest Road, police said.

He was due to move out of a house at 4100 Leitrim Rd. and was in the process of moving into a different rental house at 1248 Walkley Rd. when both went up in flames hours apart on Sunday, Sgt. Dave Christie told CBC News. 

No one was injured in the fires but both homes, which have different owners, were heavily damaged.

Nicholas was initially admitted to hospital for pre-existing medical issues and held for a psychiatric assessment, police said. On Wednesday he was charged with two counts of arson after passing the psychiatric assessment.

He has since been released from custody, police said.

Nicholas was previously convicted in the death of his wife, who drowned while on a canoe trip. Newspaper archives from the time reported that his 19-year-old wife, Jacqueline, was pregnant when she drowned in the Ottawa River in July 1957.

Shortly before his release from prison, Nicholas was convicted of instigating a prison riot and spent more years in prison, much of it in solitary confinement.

1st fire on Walkley Rd.

The first fire broke out just after 9 a.m. Sunday at 1248 Walkley Rd., a two-storey house near Bank Street.

1248 Walkley Road Ottawa fire arson police cruiser Feb 28 2016

A witness reported that a man was seen leaving the fire scene at 1248 Walkley Rd. in a van. A suspect was identified and was arrested on Highway 417 later Sunday afternoon, after another fire on Leitrim Road. (Carmen Ciubotariu)

Neighbours told firefighters there had been an explosion, but on Sunday investigators hadn't determined whether the explosion was a result of the fire or whether it caused the fire, said district chief Scott MacLennan.

The fire caused an estimated $325,000 in damage, according to Ottawa Fire Services.

No one was home and no one was injured.

Christie said Nicholas began renting the house in January and was in the process of moving in.

2nd fire broke out 15-minute drive away

The second fire happened nearly four hours later at 4100 Leitrim Rd., a house near Ramsayville Road that's about a 15-minute drive from the Walkley Road fire.

4100 Leitrim Road arson Ottawa fire Feb 28 2016

Nearly four hours after the fire on Walkley Road, firefighters were called to another suspected arson at 4100 Leitrim Rd., a 15-minute drive away from the first fire. (Scott Stilborn/Ottawa Fire Services)

Again, no one was home and no one was injured. A German shepherd named Tequila ran out of the home when firefighters entered and was unharmed.

The fire caused an estimated $350,000 in damage, the fire department said.

A witness of the Walkley Road fire told investigators a man was seen leaving the area in a van.

Nicholas had lived at the house for 20 years, Christie said. He added that Nicholas was unhappy with his living situation but did not elaborate.

Police are waiting for forensic reports to determine whether or not an accelerant, such as gasoline, was used to set the fires.

Charity work

In 2005, CBC News profiled Nicholas in a report about the Canadian Office of Human Rights, a charity that worked to help ex-convicts find work. Watch the report below.

CBC Ottawa report on Gaston "Nick" Nicholas from 20056:16