When you let a crime go unpunished, you permit it to happen again. Friendship (or appeasement) of a country doesn't mean you permit them to kill your citizens.
I hope Imran Khan takes a serious note of this incident and punishes the people involved in it. Not everyone who works for USA is covered by the Geneva convention. For God sake stop sacrificing your law because lawbreaker was paid by Americans.
It's a very complicated situation. It's quite depends on two things. 1.) Was the vehicle involved is on diplomatic plate. 2.) Was the vehicle involved is on official consulate business.
Under Vienna Convention on Diplomatic Relations 1961 (most people would misidentify it as Geneva Convention) Article 31 and Article 37, it outline how Criminal Immunity (or so called Diplomatic Immunity) are applies to Diplomat and their agents .
Article 31
1.A diplomatic agent shall enjoy immunity from the criminal jurisdiction of the receiving State. He shall also enjoy immunity from its civil and administrative jurisdiction, except in the case of:
(a) A real action relating to private immovable property situated in the territory of the receiving State, unless he holds it on behalf of the sending State for the purposes of the mission;
(b) An action relating to succession in which the diplomatic agent is involved as executor, administrator, heir or legatee as a private person and not on behalf of the sending State;
(c) An action relating to any professional or commercial activity exercised by the diplomatic agent in the receiving State outside his official functions.
2.A diplomatic agent is not obliged to give evidence as a witness.
3.No measures of execution may be taken in respect of a diplomatic agent except in the cases coming under subparagraphs (a), (b) and (c) of paragraph 1 of this article, and provided that the measures concerned can be taken without infringing the inviolability of his person or of his residence.
4.The immunity of a diplomatic agent from the jurisdiction of the receiving State does not exempt him from the jurisdiction of the sending State.
Article 37
Article 37
1.The members of the family of a diplomatic agent forming part of his household shall, if they are not nationals of the receiving State, enjoy the privileges and immunities specified in articles 29 to 36.
2.Members of the administrative and technical staff of the mission, together with members of their families forming part of their respective households, shall, if they are not nationals of or permanently resident in the receiving State, enjoy the privileges and immunities specified in articles 29 to 35, except that the immunity from civil and administrative jurisdiction of the receiving State specified in paragraph 1 of article 31 shall not extend to acts performed outside the course of their duties. They shall also enjoy the privileges specified in article 36, paragraph 1, in respect of articles imported at the time of first installation.
3.Members of the service staff of the mission who are not nationals of or permanently resident in the receiving State shall enjoy immunity in respect of acts performed in the course of their duties, exemption from dues and taxes on the emoluments they receive by reason of their employment and the exemption contained in article 33.
4.Private servants of members of the mission shall, if they are not nationals of or permanently resident in the receiving State, be exempt from dues and taxes on the emoluments they receive by reason of their employment. In other respects, they may enjoy privileges and immunities only to the extent admitted by the receiving State. However, the receiving State must exercise its jurisdiction over those persons in such a manner as not to interfere unduly with the performance of the functions of the mission.
So, in a TLDR version, Article 31 give Diplomat Agent (which explained below) immunity from criminal prosecution, and article 37 defined as long as that person is
1.) A member or technical staff to the mission, or spouse to a member or technical staff to the mission.
2.) Not a permanent resident or citizens of the host nation (In this case, not a PR of Pakistan or Citizen of Pakistan)
3.) Working on behalf, or act performed in the course of their duty.
That person also enjoy the so called Diplomatic Immunity.
Now, how these comes to term is basically largely depends on how US spin the story, he could be a driver and when he hit the other car and killed the women, if it is under "Official Duty", then that driver would be immune from prosecution, now, what is "Official Duty"? That's vary between deliver diplomat cable to another consulate to minor thing like running errant for the ambassador (Like getting milk or stuff)
So, if the person is not a Permanent Resident/Citizen of Pakistan, Driving a Diplomatic Registered Vehicle, was on official duty, then chances are he will let off the hook.
A motorcyclist was killed in Britain by an American diplomats wife in her over speeding vehicle on the wrong side of the road. She was allowed to leave and there is no proceeding against her.
It's the diplomatic immunity bullshit that's saving them.
That's actually not a valid case and most legal professional in the field (as far as I know) is saying the UK got that wrong.
Yes, that women is a spouse of a US Diplomat, but she was not on any official duty. She may be on home duty like buying groceries for their household, but she was not on official duty (Notice that if she is buying groceries for the ambassador, that would be official duty), hence the immunity from criminal prosecution does not applies.
On the other hand, British Police do not know this does not applies and let her go, and she in turn leave UK and went back to US, and now, this has become extradition matter. UK can request an extradition (they did actually) but it is up to US to heed the call. And more than likely, they won't.