The size of the reward, publicised throughout the country yesterday, appeared to be an attempt to winkle out an informant within Mexico's drug cartels, but was also a measure of the public terror that they inspire.
The announcement came as the authorities sought to counteract scepticism among Mexicans, who are finding it hard to believe the official version of events - that the cardinal was killed by mistake as he sat in his car awaiting the arrival of a Vatican representative. He was hit 14 times by bullets fired from a few feet away.
Prosecutors insisted that Juan Jesus Posadas Ocampo, Mexico's second most senior churchman, was shot to death by gunmen who mistook him for a gangster - possibly the notorious drug lord, Juaquin 'El Chapo' Guzman, whom they were allegedly sent to the airport to kill.
Although the chances of a senior and well-known Catholic cleric being confused with a gun-brandishing thug seem remote, officials supported their claim with a list of reasons. According to the state attorney-general, the cardinal's car - a sparkling white 1993 Ford Gran Marquis - is the kind of vehicle favoured by the drugs traffickers. The churchman was also clad in a black suit, popular attire among the gangsters.
Furthermore, the attorney-general argued, the gunmen came equipped with a large supply of weapons - which included grenades, rifles, pistols, and flak jackets - far more than they would have needed had they intended to kill the cardinal, who travelled without bodyguards. Guzman, on the other hand, was always protected by around 10 armed henchmen.
No mention was made of the fact that the cardinal, who publicly denounced the drug traffickers, was 66 years old - around 20 years older than Guzman - and was wearing a large chain around his neck and a dog collar.
Nor was there any explanation as to the whereabouts of the airport's police during the gunfight, or why almost all the gunmen managed to escape by car into west Mexico.
Officials blame the deadly gunfight on a feud between Guzman and the Arellano Felix brothers, bosses in a rival drug mafia that operates in Tijuana near the US border. All three, and an associate of Guzman's, were named on posters distributed nationwide advertising the dollars 5m reward.
The authorities say that a group of 15 gunmen were dispatched to Guadalajara - by a shadowy associate of the brother's known as 'El Popeye' - with instructions to murder Guzman. They appeared to have been settling old scores over drug-running territory: in November, Guzman was allegedly behind an attempt to kill the brothers when armed men stormed a disco and mowed down six people.
Several thousand people stood in the tree-lined square outside Guadalajara's cathedral yesterday, sheltering from the sun under black umbrellas, listening to the funeral Mass echoing from loudspeakers. In surrounding market stalls and shops, passers-by crowded round radios and television sets broadcasting the service.
There were calls for a credible explanation and an inquiry. 'Powerful political and economic interests are related to the death of Posadas Ocam po,' said Nicolas Lopez, president of the Latin American Bishops Council. 'It won't make any difference,' said Juan, a local worker. 'The traffickers have penetrated the government and police at so many levels.'