Hundreds of people paid their respects to the Italian youth in Rome on Tuesday.
Mourners were provided with public space to file past Sandri's coffin.
Hundreds of friends, relatives and Lazio fans, many wearing scarves with the Roman club's colours, attended along with several Lazio players, football officials and Giovanna Melandri, the Italian sports minister.
"Let's hope that we'll never again witness such a tragedy," said Lazio player Luciano Zauri.
Death sparked riots
Italian police have so far arrested 25 people suspected of involvement in the riots which followed Sandri's killing.
Initial reports of the shooting said police had intervened to stop a scuffle between Sandri's group of Lazio fans and a group of Juventus fans.
The unnamed policeman told the Corriere della Sera newspaper that he had accidentally fired the fatal shot as he was running, just seconds after firing a warning round in the air.
But Giuliano Amato, the interior minister, told the Italian parliament: "It seems definitively established that the shot came with his arms outstretched from the other side of the highway.
"It remains to be understood why."
He said the officer also should have put his pistol back in his holster after the first warning shot.
Giogio Napolitano, the Italian President, expressed his solidarity with the man's family and called on officials to shed full light on the "tragic and absurd" circumstances of his death.