Man sentences to life in prison after murder of transgender
She was stabbed 13 times in her Buenos Aires flat in October 2015.
Gabriel David Marino, 25, has become the first person in Argentina to be sentenced under new legislation on crimes against transgender people.
Human rights groups say Latin America accounts for the greatest number of transgender murders worldwide.
Mr Marino said he had sexual encounters with the victim in exchange for illegal drugs. But he denied killing her.
‘Light that guides me’
Ms Sacayán was a well-known activist for lesbian, gay, bisexual and transgender (LGBT) rights.
She was the first Argentine citizen to receive a new national identity card after applying to have her gender changed.
Argentina’s president at the time, Cristina Fernández de Kirchner, handed her the card personally.
Ms Sacayán was 40 when she was killed.
The trial at the Supreme Court building was followed by dozens of friends, relatives and fellow campaigners.
“My sister was an example and she taught me to fight for my rights. She is a light that guides me,” her sister, Sasha Sacayán, told Clarín newspaper.
Central and South America accounted for 74% of the 2,016 murders of transgender and gender-diverse people reported worldwide between January 2008 and December 2015, according to activist group Transgender Europe.