"All the facts indicate his involvement," Interior Minister Manuel Valls declared after Dekhar's arrest in an underground carpark in a town north-west of Paris.
CCTV footage and DNA tests have satisfied police that they have the man who has eluded them since Friday, when he attacked the headquarters of BFMTV, going on to shoot a photographer at the Libération newspaper and fire shots outside the headquarters of the Société Générale bank.
The photographic assistant, known as César, is out of the coma he was in after being shot in the chest, according to Libération's director of publications, Nicolas Demorand, who said on Thursday that the arrest was an "enormous relief".
Hollande on Thursday hailed the "efficacity of the police and the justice system", saying that they had "prevented the worst happening again".
Dekhar was tracked down after a friend, who was putting him up, recognised the photos distributed by the police and told them that Dekhar had told him that he had done "something stupid".
Police found him semi-conscious in a car in Bois-Colombes, north-west of Paris.
"Everything seems to show that he tried to commit suicide," Valls said.
"One or more letters" written by Dekhar have come to light, the minister said.
Although BFMTV says that one of them was an incoherent ran about the situation in Libya, Syria and the rest of the Arab world, Valls said it was not possible to attribute a political motive to the crimes "at this point".
Dekhar, who apparently once served in Algerian military intelligence, served four years in prison for providing a shotgun used in a 1994 raid on a car pound that went disastrously wrong, ending in the death of one of the perpetrators, a taxi driver and three police officers.
The other perpetrator, Florence Rey, claimed that Dekhar had helped plan the raid but he was only found guilty of supplying the firearm and jailed for four years.
Rey was sentenced to 20 years and released in 2009.
The motives for the raid were never clearly established, although Dekhar, Rey and her boyfriend Audry Maupin, who died while trying to flee, were believed to be close to small far-left groups known as autonomes.