On Wednesday, the 25th, as the brethern were beginning to raise one of the capitals, having neglected to fasten the guys, the crane fell over with a tremendous crash, breaking it considerably. As soon as it was perceived that the crane was falling, the hands fled to get out of the way. One of the brethern, Thomas Jaap, running directly in the course of the falling crane, barely escaped being killed. The crane struck the ground and was within a foot of striking his head. This circumstance hindered the workmen some; but in a few days the crane was mended, reared, and the brethern again went to work on it.
...Jacob Morris ... stated that Miles had come with the intention of setting fire to the lumber, that the building might be hindered, as Lyman Wight had said the temple never would be built.
Whether this was the intention of Brother Miles or not we could not learn satisfactorily. However, enough was known to induce the authorities of the Church to advise the committee to have some of the old police guard the lumber and the temple night and day. The police have continued to guard it to this time. There has since been many threats thrown out from the Rigdonites and other sources that the temple never should be built, and no doubt an attempt would have been made to set fire to it if it had not been well guarded all the time.
[Fillerup, Robert C., compiler; William Clayton Nauvoo Diaries and Personal Writings, A chronological compilation of the personal writings of William Clayton while he was a resident of Nauvoo, Illinois. http://www.boap.org/LDS/Early-Saints/clayton-diaries]