Masiello, 27, collapsed dejectedly on the grass after his own-goal sealed a 2-0 defeat for Bari, which was already facing relegation from Italy's Serie A.
But the player has now admitted to investigators that he was offered at least €50,000 (£41,600) to turn the ball into the net to ensure Bari lost and help secure Lecce's survival in Serie A.
Magistrates who arrested Masiello and placed eight of his former Bari team-mates under investigation are now studying the team's final games of last season. They suspect matches thrown by the side from Puglia, in southern Italy, may have determined which teams went down and which qualified for Europe.
The investigation is the latest twist in a rumbling match-fixing scandal which threatens to throw Italian football into disarray.
The Bari players, wrote judge Giovanni Abbattista, "were more or less 'on the market', and not in the footballing sense of the term". Treated as idols by fans, they were no more than mercenaries, he said.
Despite its reputation for attractive football, Bari could not compete with Serie A's big guns last year and players reportedly feared the club would not pay their wages as it slipped into the relegation zone.
Magistrates have suggested management at Bari and Lecce were privy to the fixing of their match, but Bari's sporting director, Guido Angelozzi, denied any role.
Investigators suspect players of being approached to throw other games by a mysterious Balkan group of gamblers known as The Gypsies, which is suspected of paying off players from a number of Italian sides.
Last June, the Italian government established a match-fixing taskforce as the former Atalanta captain and Italy midfielder Cristiano Doni was banned for three and a half years for match fixing in Serie B, the former Lazio and Italy player Giuseppe Signori was banned for five years and 15 other players were banned for between one and five years.
Masiello's arrest moves the scandal out of Serie B and places it firmly in Serie A. In an interview last month with Italy's La Repubblica, Macedonian Hristiyan Ilievski, the alleged head of The Gypsies, claimed he had approached Bari players when he heard the team was destined for relegation.
Masiello, he said, "seemed to have clear ideas about what he wanted and what he had to do".
Ilievski claimed that in Bari the local mafia was already involved in match fixing. Bari players have claimed they were under pressure from the heads of "ultra" groups of supporters to throw games at the end of the season to assist betting scams.
The Italian football federation, which is recovering from a previous match-influencing scandal which led to relegation for the top side, Juventus, called the arrests "sensational developments" and said it would take swift action against any players who were found guilty.
