Full article from The Christian Standard can be read here
“About this time a new supply of preachers came on from New York with some of the witnesses of the Book of Mormon, among them Parley Pratt and Martin Harris. Soon afterwards they began to have visitations of angels among them. I was suspicious of these angels from the first. When they partook of the sacrament they always did so at night. In preparation for this they would exclude everybody from the room but the leaders and would then hang up blankets and quilts at the windows. When all was ready they would open the doors and let the people in. I determined to stay through one of their services of the sacrament, so a friend and I went to meeting with that intention. He went to sleep just before the time to exclude the people, and I became possessed of a deaf-and-dumb devil and they could not make me understand anything. After a time they decided to leave us alone and go on with their ceremony. My companion awakened and we saw the whole performance. I became satisfied that their power was in the wine, so I tried to steal a bottle, and would have succeeded if I had been wearing the cloak I usually wore.
Persons coming from abroad were invited to stay with them over-night and were invariably baptized by them in the morning. Soon they began to invite residents to stay all night with them, and they were also baptized next day. In this way they began to make converts again and I wondered how it was. I asked some of them what had made them change their minds, and their answer was, ‘If you could see what we have seen you would be convinced too.’
‘But what have you seen?’ I asked.
‘Oh, we dare not tell!’ they replied.
This aroused my suspicion still more, and I determined to ferret the matter out if possible. For this purpose I ceased all opposition to them and became very grave and sober in their meetings. Soon they began to entertain hopes of my conversion and my friends began to be very uneasy about me. Although they talked to me about it and solemnly warned me, I kept my own counsel. I soon got an invitation from the Mormons to stay all night with them. As this was what I was working for I gladly accepted, but so many strangers came from abroad that they could not accommodate me. They, therefore, requested me to put it off until the next night, and I reluctantly complied. The next day Bro. Matthew Clapp came from Mentor to see me, and taking me into the field after school reasoned with me and pleaded apparently in vain. But when he wept and worked on my feelings and sympathies, I told him my suspicions and plans enjoining the strictest secrecy upon him until I should have the opportunity to test the matter. The next night the same difficulty occurred and I was again requested to wait until a later night. In the meantime Brother Clapp could not forbear to relieve the minds of some of the anxious brethren, and the story got out so that the Mormons heard it and the plot was spoiled.
I then stated publicly my suspicions. I said I had studied the black arts, or necromancy, and knew just how their angels were made, and showed how it could be done. I stated that if I had succeeded in getting to stay there all night, I would have had a wrestle with the angel, and that I was sure it would have been of flesh and blood. Perhaps, however, it was best that I failed in my plan and it may be that I was foolhardy, for they might have taken my life rather than be exposed.”