Helric Fredou, 45, the deputy director of the regional judicial police in Limoges turned his gun on himself last Wednesday night, hours after Cherif and Said Kouachi killed 12 people in an Islamist rampage, including two policemen.
"We are all stunned. He was someone who was very humane and close to people," said Pascal Cayla of the Alliance union.
Colleagues said Mr Fredou had been deeply affected by the suicide of the number three of the Limoges judicial police in 2013 after he discovered the body. His colleague had left a note citing "personal reasons".
Since the twin attacks last week that rocked France and left 17 people dead, there has been an outpouring of support for the country's police force, which polls regularly suggest has a poor image among many French.
There were banners reading "We love the police" at Sunday's huge march in Paris and cities around France.