Estermann and his wife were murdered in his apartment in Vatican City on 4 May 1998, the same day he was confirmed in his position after serving as acting commander for over a year.

[1] In 1981, Estermann had been one of the bodyguards guarding the popemobile when Pope John Paul II was shot in an assassination attempt, where he was photographed.

[1] On 4 May 1998, the same day he was confirmed in his position, Estermann and his Venezuelan wife, Gladys Meza Romero, were shot and killed by 23-year-old Swiss Guard Vice Corporal Cédric Tornay.

[4][1] Tornay had earlier been reprimanded by Estermann for spending a night outside Vatican City without permission, and had been passed over for a medal routinely awarded to Guards after three years of service.

In a 2011 history of the modern Vatican's military and police forces, Professor David Alvarez, of the Department of Politics at St. Mary's College of California, summarizes the various conspiracy theories before concluding that they "either remain unsubstantiated or have been thoroughly discredited".