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Six others accused of involvement have been acquitted, the lawyer said. They included two of Baloch's other brothers, her cousin, a neighbor, a driver, and a Muslim cleric.
Waseem admitted in a 2016 media conference organized by police that he strangled his 26-year-old sister due to her social media activities.
Baloch had posted risque Facebook posts in which she spoke of trying to change "the typical orthodox mindset" of people in Pakistan. She faced frequent misogynist abuse and death threats but continued to post provocative pictures and videos.
Baloch, whose real name was Fauzia Azeem, was described as Pakistan's Kim Kardashian and had built a modeling career on the back of her social media fame, but drew ire from many in the conservative South Asian nation.
Her killing sent shockwaves across Pakistan, triggered an outpouring of grief on social media, and prompted the government to tighten laws to ensure that killers would not walk free if family members forgave them.
Local media had reported in August that Waseem's parents had forgiven their son and asked for him to be acquitted. Reuters was unable to reach them for comment.
"It takes too long, people forget," said Farzana Bari, a women's rights advocate and founder of Pakistan's first gender studies department at a university, adding that even the high-profile Baloch case had taken over three years to be resolved.
Though rights groups say reliable data is hard to establish, the Human Rights Commission of Pakistan found at least 300 cases of "honor killing" in 2018.
Many advocates say the actual number is far higher, with the Honour Based Violence Awareness Network estimating that Pakistan accounts for about a fifth of the 5,000 honor killings globally each year.