An 18-year-old girl from the Hindu community was gunned down on Monday near the Chhuahra Mandi area of Sukkur, the police said.
According to Sukkur Station House Officer (SHO) Bashir Jagirani, the assailant — identified as Wahid Bux Lashari — and two of his accomplices broke into Pooja Kumari's house and opened fire on her. Officials said Lashari wanted to marry the teenager but she refused.
The victim's father, Sahib Oad, lodged a first information report (FIR) against the suspects under Section 34 (acts done by several persons in furtherance of common intention), Section 302 (punishment for murder), and 337H(ii) (punishment for hurt by rash or negligent act) of the Pakistan Penal Code.
The police arrested Lashari today and presented him before a local court, which subsequently remanded him into police custody for 10 days.
Later, PPP Chairperson Bilawal Bhutto-Zardari issued a condemnation and said Sindh police had arrested all suspects in the case. He also lauded Sindh police for the "expeditious arrests".
In a statement, Bilawal said the relevant authorities should make sure that the culprits were meted out stringent punishments.
Dawn.com could not independently verify that all suspects had been arrested.
Bilawal also expressed solidarity with Kumari's family and said anyone intending to harm the oppressed would have to face the PPP first.
Kumari's murder drew condemnation on social media, with #JusticeforPooja trending on Twitter.
PML-N President Shehbaz Sharif called the murder "heinous and condemnable" and said such incidents "represent our collective failure and put our whole society to shame".
"No girl deserves to go through this. High time we thought why we continue to hit lows one after the other," he tweeted.
Former MQM leader Raza Haroon was among those who demanded justice for the slain girl. He urged Pakistan Peoples Party Chairman Bilawal Bhutto-Zardari to take action, calling it the "worst form of human rights violation and persecution of religious minorities in Sindh".
Activist and lawyer Jibran Nasir criticised the provincial authorities, saying: "Under the PPP government, child marriage laws aren't worth more than the paper they're printed on.
"Doors to forced conversion of minor girls are open because child marriages are facilitated by corrupt and ignorant [officials]," he added.
Nobel Prize laureate Malala Yousafzai's father Ziauddin called the murder "disgusting" and a "heinous crime", adding that "we all must speak up to demand justice for the bravest Pooja Kumari."