15 people were killed and 70 injured on March 15 2015 at St John's Church and Christ Church in Youhanabad, an area in the city of Lahore, when two bombs went off outside them.
Christian Solidarity Worldwide (CSW) has said that it wants a full, impartial investigation by Pakistan's authorities and for the perpetrators to be brought to justice.
Following the 15th March 2015 bombing, protestors filled the streets in the predominantly Christian area of Lahore.
Two Muslim men who were suspected to be connected to the bombings were lynched by a mob.
The government launched an investigation to find those behind the lynching and CSW says around 100 young men have been arrested and are facing trial in the fast-track anti-terrorists courts.
It is reported that arrests are still being made in connection with the atrocity.
Doubts have been raised about police impartiality and CSW says that police have relied on video and mobile phone footage and made arrests without warrants.
There is also concern being raised about the excessive force used by police during their investigations.
One man who was detained told CSW that "the police arrested all the youth, telling these young men that they were on a list.
"They were randomly picking up suspects to fulfil a quota, there was pressure from the Chief Minister to make arrests so the police were out to arrest anyone they could get."
The attacks in Lahore raised worries about the security of churches and other Christian institutions in the country, and CSW has urged Pakistan's government to act on the recommendations of a 2014 Pakistan Supreme Court judgement.
It set up a special taskforce for minorities to take effective measures to curb hate speech and develop appropriate teaching in schools to promote religious and social tolerance.
CSW's Chief Executive Mervyn Thomas said: "On the first anniversary of the double church bombing in Youhanabad, no one has yet been held to account for this crime.
"We urge the Pakistani Government to launch a full enquiry into the bombings and to ensure that the police adhere to due process both in bringing the perpetrators to account and in apprehending those who killed the two Muslim men in the aftermath of the attack.
"We also urge the government to enact the Supreme Court recommendations to ensure that the rights of religious minorities in Pakistan are upheld."