A pastor at a Lutheran church in San Mateo was arrested after allegedly delivering letters full of shooting threats to a San Carlos church where he was formerly a congregation member, authorities said.

In four separate instances between Jan. 7 and Jan. 16, Paul Michaelson, 79, dropped off letters to the Holy Trinity Church in San Carlos detailing his plans to shoot members this Sunday, according to San Mateo County Sheriff’s Office Detective Rosemerry Blankswade.

He was arrested at his home in San Carlos on Thursday night on suspicion of terrorist threats and violation of civil rights by threat of force. A search of his home did not reveal any weapons, Blankswade said.

As of Thursday, Michaelson served as a part-time outreach pastor at Hope Lutheran Church in San Mateo, which is part of the same synod or network of Lutheran churches as Holy Trinity, church officials confirmed.

The wider Lutheran community — which counts 185 churches in its Northern California Sierra Pacific Synod — was “shocked” to learn of Michaelson’s arrest, Bishop Mark Holmerud told this news organization.

“Understanding that an arrest is not a conviction, we are at a loss to understand why anyone would attempt to disrupt the ministry of a congregation whose intent is to be a haven of peace, inclusivity and reconciliation in the community,” Holmerud added in a statement.

Michaelson’s letters allegedly chronicled a “deeply rooted” anger against Holy Lutheran that brewed during his time as a congregation member at some point in years past, Blankswade said.

Investigators declined to share more about the grievances, but they resulted in specific threats against church members pegged to this Sunday, Blankswade said, adding that there is no evidence at this time that the threats stemmed from a documented mental illness.

After the congregation reported the threats, investigators obtained church security footage and identified him based off accounts of church members who know Michaelson.

“It sounded like he did not get the help he was seeking, and because of that he felt deeply wronged by the church,” Blankswade said.

Neither San Mateo nor church officials could confirm the time period that Michaelson attended Holy Trinity. According to his LinkedIn, he has served as a part-time pastor at Hope Lutheran since 2004 and once attended St. Olaf College in Minnesota.

As of Friday morning, Michaelson was still listed as pastor on Hope Lutheran’s website. Hope Lutheran did not immediately respond to a request for comment.

Credible threats against religious communities are uncommon in San Mateo County, and there have been no cases in recent memory in which the suspect was an active member of the community, Blankswade said.

As of Friday morning, Michaelson was no longer listed in custody.