Robert Groen (Winnipeg Police Service)

One of the men arrested in Mexico in the abduction of two Winnipeg children has been returned to Canada for prosecution.

Robert Groen was extradited on July 19 and is back in Winnipeg, city police announced Tuesday.

He was arrested May 25 in Guadalajara, Mexico, along with Kevin Maryk, who is the biological father of the abducted children.

Groen has been charged with two abduction-related offences. It is not known when Maryk is expected to be brought to Canada, but police told CBC News they are actively pursuing the matter.

Kevin Maryk (Winnipeg Police Service)

Abby and Dominic Maryk were five and seven years old, respectively, when they went missing in August 2008.

They were on a two-week vacation as part of a court-approved visit with their father but were never returned to their mother, Emily Cablek, who has legal custody.

The children were found May 25 near a townhouse complex in Guadalajara.

Abby, who is now nine years old, and Dominic, now 11, have since been returned to Cablek and are living at home in Winnipeg.

Cody McKay remains at large. (Winnipeg Police Service)

Investigators are still looking for Cody McKay, 23, although It's not clear what McKay's role in the case might be. He is the nephew of Kevin Maryk.

A Canada-wide arrest warrant has been issued for McKay but police said they believe he remains somewhere in Mexico.

Winnipeg police said the children had been moved at least five times over the past four years to different locations in Mexico.

Christy Dzikowicz of the Canadian Centre for Child Protection has said the children lived in poor conditions in Mexico, as they had no schooling, no friends and no medical assistance during the time they were hidden by their father.

They were never taken out during the light of day and only breathed fresh air when they were allowed out at night, she added.

Juan Manuel Estrada of FIND, a Mexican missing persons foundation that helped authorities track down the Maryk children, told CBC News the kids were kept in a three-bedroom condominium, surrounded by four guard dogs and numerous security cameras.