A Utah father was days away from seeing his four children — the culmination of a years-long visitation battle — when he learned they had been killed in a heinous crime their grandmother is accused of committing.

Brady Harmon said he was scheduled to pick up his children on Wednesday and return them to their mother in New York on Sept. 1, as part of a court-ordered parenting plan. Instead, Salt Lake City police delivered devastating news that his children — Harper Harmon, 13; Hudson Harmon, 11; and 10-year-old twins Gavin and Gracelynn Harmon — were found dead in a Mechanicville, New York, apartment.

The children’s mother, Sarah Myers, 44, and their maternal grandmother, Amy Steadman, 64, were also found dead, Mechanicville police said.

Officers were dispatched to the apartment after a neighbor reported not having seen Steadman for some time. Police Chief William Rabbitt said at a Thursday news conference that Steadman lived in the apartment, while Myers and the children lived separately within the same building.

“I don’t know what happened,” Harmon said in a phone interview Friday. “I have speculations, but not to be able to see my kids — that’s the part that sucks the most.”

Rabbitt said one of the children is believed to have suffered fatal sharp-force injuries. Evidence also points to intentional poisoning, including what he described as “numerous prescription and over-the-counter medications.” Causes and manners of death for all six victims remain pending further testing.

A handwritten note found in the apartment “strongly suggests that Amy Steadman was involved in the deaths,” Rabbitt said, declining to discuss the nature of the note.

Harmon said he learned of Steadman’s suspected role by watching the news conference. “I have no idea why they could think it would be her,” he said. “The handwritten note, that’s one thing, but she had nothing to lose or gain by my kids coming out here.”

Harmon said that he had been fighting for visitation rights for years. Court documents obtained by NBC News show the couple separated in November 2019, with their divorce finalized the following year. After the separation, Myers relocated to New York with her mother and the children.

Under the custody agreement, Harmon was entitled to have the children from July through September, along with regular FaceTime calls. But he said Myers repeatedly blocked both. The last time he saw his children in person was in 2019, he said.

“There was always something that came up — she would find a way out of it,” he said. “Eventually, I had to get a different lawyer just to enforce the parenting plan.”

During the FaceTime calls he was permitted, Harmon said he could speak with all four children together for roughly 15 minutes with Myers present in the room.

He recalled small, ordinary moments: Gavin showing off things he had built, Gracelynn and Harper sharing drawings they’d made for him.

He said he never suspected that anyone would harm his children, and that in recent months Myers had seemed to be honoring the parenting plan more consistently. Separate court documents show that Myers was scheduled to appear in Utah court on Monday. Harmon said they were supposed to discuss the parenting agreement before he got his children.

“This is not something anyone could prepare for,” he said.