The 19-year-old girl was killed by her brother on February 8 in Pano Aqil after the local jury declared her a "sinful woman" as she was found to be having an affair with a relative.
"The local jury decided that the girl had brought dishonour for her family and declared her as sinful," Shaikh said.
He said the family of the girl had initially tried to give the impression that she had committed suicide.
"But we have now arrested the brother and father and two landlords who have confessed to their involvement," he said.
Such 'honour killings' are common in Pakistan in poor communities in urban areas and cities and more recently there have been several cases reported in Karachi where local 'Jirgas' condemned victims to death.
Last December, the so-called honour killings of 18-year- old Ghani Rehman and 15-year-old Bakhtaja in Karachi shocked the country as both were condemned to death by electrocution by a local Jirga or elders' council for eloping together.
The families including the fathers and uncles of the two teenagers carried out the killings.
The Human Rights Commission of Pakistan says around 650 "honour killings" have been carried out in Pakistan annually in the last decade and the figures could be much higher as many cases go unreported.