Prince William says he is “deeply saddened” following the murder of a South African park ranger he spoke with last year, calling for justice in a personal note he tweeted on Wednesday after the news broke.

“I’m deeply saddened to learn of the killing of Anton Mzimba who I spoke to in November,” he wrote.

Mzimba met with the Duke of Cambridge, who is deeply involved in conservation and wildlife anti-poaching efforts, last year to discuss how technology can aid in identifying the trafficking of illegal wildlife products.

“Committed and brave, rangers like Anton are central to the conservation of Africa’s fantastic wildlife,” he said, adding “Those responsible must swiftly be brought to justice. My thoughts are with his family.”

William signed off with a “W” on the tweet, to indicate that it was a personal tweet sent by him.

I’m deeply saddened to learn of the killing of Anton Mzimba who I spoke to in November. Committed and brave, rangers like Anton are central to the conservation of Africa’s fantastic wildlife. Those responsible must swiftly be brought to justice. My thoughts are with his family. W

— The Duke and Duchess of Cambridge (@KensingtonRoyal) July 27, 2022

Mzimba was the head of ranger services at the Timbavati Game Reserve, where he spent the last 25 years of his career and fought against wildlife crime.

In a statement following his death, those at the game reserve said in tribute to their “fallen hero” that they “lost a special family member, a rhino warrior, a wildlife guardian, a loved one, a comrade, a friend, and a true legend.”

“Today is a heartbreaking reminder of the huge challenges our wildlife protectors face and just how incredibly important it is to continue to support them in every way we can,” the statement added, thanking Mzimba for giving “his life and love to the wildlife and people of the Timbavati. He will be profoundly missed but never forgotten.”

The ranger was reportedly shot and killed outside of his home, the non-profit organization, Helping Rhinos, said.

“This follows recent death threats and highlights the daily threat facing rangers,” the organization said.

Head of Ranger at Timbavati, Anton Mzimba, was shot and killed outside of his home last night. This follows recent death threats and highlights the daily threat facing Rangers.

Our deepest condolences to Anton’s loved ones and co-workers at this difficult time pic.twitter.com/fRayloiFjB

— Helping Rhinos 🦏 (@HelpingRhinos) July 27, 2022

The attackers who shot and killed Mzimba also injured his wife, who is currently in the hospital, according to The UK Times.

An employee at the South African Wildlife College, where Mzimba worked with fellow rangers, told The Times of the possible motivation for his killing.

“The rhinos on the Timbavati were well protected by his team,” Ashwell Glasson said of Mzimba’s work. “He had become a major obstacle to the poachers who wanted to take his area. So there was pressure, there were threats, but he faced it all down.”