Police detectives are investigating the slaying of a human rights activist and his wife, Haitian authorities said Monday.

Police spokesman Gary Desrosiers told Radio Caraibes that Daniel Dorsinvil and Girldy Lareche were killed Saturday by a lone gunman as they walked through a residential neighborhood in the capital, Port-au-Prince.

Desrosiers didn't cite a motive for the killing, though he acknowledged reports that the couple were either killed in a robbery or targeted because of the husband's activism.

Dorsinvil was coordinator for the Platform of Haitian Human Rights Organizations, one of Haiti's lesser-known advocacy groups.

President Michel Martelly's administration condemned the killing in a communique issued from its press office Monday.

Other rights activists in Haiti have been targeted for their work.

A lawyer who was investigating corruption allegations last year was locked up overnight. Supporters erected burning barricades in downtown Port-au-Prince on his behalf and then physically escorted him out of the courthouse.

Other human rights lawyers have reported receiving death threats over the phone and being followed.

The New York-based Human Rights Watch this year said election delays, natural disasters and a deadly cholera epidemic are hindering the Haitian government's ability to tackle long-standing rights problems.