An assassination attempt by bombing against Álvaro Obregón (which only wounded the ex-president) in November 1927 provided the state with a pretext to capture Pro and his brothers Humberto and Roberto. A young engineer who was involved and confessed his part in the assassination testified the Pro brothers were not involved. Miguel and his brothers were taken to the Detective Inspector's Office in Mexico City.Taken from: http://en.wikipedia.org/wiki/Miguel_Pro
On November 23, 1927, Fr. Pro was executed without trial. President Calles gave orders to have Pro executed under the pretext of the assassination, but in reality for defying the virtual outlawing of Catholicism. Calles had the execution meticulously photographed, and the newspapers throughout the country carried them on the front page the following day. Presumably, Calles thought that the sight of the pictures would frighten the Cristero rebels who were fighting against his troops, particularly in the state of Jalisco. However, they had the opposite effect.
Fr. Pro and his brothers were visited by Generals Roberto Cruz and Palomera Lopez around 11 p.m. on November 22, 1927. The next day, as Fr. Pro walked from his cell to the courtyard and the firing squad, he blessed the soldiers, knelt and briefly prayed quietly. Declining a blindfold, he faced his executioners with a crucifix in one hand and a rosary in the other and held his arms out in imitation of the crucified Christ and shouted out, "May God have mercy on you! May God bless you! Lord, Thou knowest that I am innocent! With all my heart I forgive my enemies!" Before the firing squad were ordered to shoot, Pro raised his arms in imitation of Christ and shouted the defiant cry of the Cristeros, "Viva Cristo Rey!" -"Long live Christ the King!". When the initial shots of the firing squad failed to kill him, a soldier shot him point blank.