Twins have the same DNA but epigenetics do have effects on this genes that are expressed, but investigation into this can mean $$$, something the government "has plenty of."
They need to look for other pieces of evidence to connect one twin to the crime. This is still tricky since they usually look pretty much alike.
What if there is only DNA? What can the police do?
We demand the the government further investigate the unlikely possibility that identical twins may be exchanging positions in classes. Through more complex dna testing they'll evaluate the integrity of Stapleton's class which may be determined as compromised.
+ AP Bio taught by THE Derda is dense; time to study
Side note: Teachers need a pay raise; they work harder than most state employees, [no] offence lazy bureaucrats