from the BYU website:
This brick building was located on Mulholland Street on the block east of the Nauvoo Temple. On the second floor of this building was located the printing press on which the Nauvoo Expositor was printed. The destruction of the press was the event which triggered a series of events culminating in the murder of Joseph and Hyrum Smith at Carthage 20 days after its publication.
Early in 1843 a group of members of the Church at Nauvoo, including Joseph Smith's second counselor and one of the presidents of the Nauvoo Stake and several business and professional people, commenced opposing Joseph Smith because of new doctrine and practices which were introduced in the Church. Foremost among these so-called objectionable tenets were the practice of plural marriage, eternal progression of man toward godhood, eternalizing of the marriage covenant, the endowment ceremony, and the political kingdom of God with its secret Council of Fifty. After these men were excommunicated from the Church in April 1844, they purchased a press and published a paper entitled the Nauvoo Expositor, the only issue appearing June 7. This first and last edition of the paper declared that Joseph Smith had become a tyrant, ruling Nauvoo contrary to American principles of separation of church and state; that he had introduced into the Church doctrine and practices which were contrary to the original teachings of the Church, particularly that secretly he was practicing plural marriage which they termed "whoredoms and abominations." They announced their intention to seek the repeal of the Nauvoo Charter so that Nauvoo might become a city governed by American standards of democracy.
The Expositor appeared on Friday afternoon, and the following morning and the Monday thereafter the city council met to consider its threat to the peace and security of the city. With the powers granted by the city charter, they declared the newspaper a nuisance, as they felt its declarations threatened the security of the city. They authorized the mayor (Joseph Smith) to see that the nuisance was abated. The Prophet instructed the city marshal to abate the nuisance which he and his men accomplished by breaking into the printing shop, throwing the press into street where it was smashed with a sledge hammer, dumping the type into the street, and burning the undistributed copies of the newspaper. Such an extralegal method of abating a newspaper was not without precedent in Illinois (though not in keeping with long established practices concerning abatement of a public press), but it was viewed as a violation to the federal Constitution which forbids destruction of property without due process of law. The city council had only the authority to abate the nuisance by suspending further publication of the paper pending a court hearing which would determine whether it was a public nuisance.
The proprietor of the paper went to Carthage and swore out a warrant for the 18 members of the city council, charging that they had violated the federal Constitution by destroying property with the resultant implication of "suppression of the freedom of the press." In response to the charge 15 members of the Nauvoo city council appeared before the justice of the peace in Carthage on Tuesday, June 25, and were bound over to the next term of the circuit court on bail of $500 each. Jointly they posted $7500 in bonds and some of them returned to Nauvoo that afternoon. Joseph and Hyrum, however, remained in Carthage to have an interview with Governor Ford. While awaiting audience with him, they were arrested on charges of treason and rioting for having used some of the Nauvoo Legion to assist the town marshal in the destruction of Expositor equipment. For this charge they were committed to the Carthage jail that afternoon.