Max has several very good points, and bluntly, is right: these are the exact situations you invest all that money in good, loyal corp troops for. Runners are designed to avoid exposing the corp, not increase the risk That said, there is a pretty simple tweak that will bypass that: make it someone else's facility. If the runners leak that it's Corp B's facility, Corp A who hired them is probably happy about it and happy that they have done their best to avoid tipping their hand that they both A) conducted a smash and grab to get the data, and B) Blared Corp B's dirty laundry all over the 'trix.
You can basically use your initial brief with a few mods:
"We've been tracking a rival bio-research facility. Something went wrong in the last five hours, and one of our informants tried to send an update and extraction call, but it got interrupted mid transmission. We don't know how it got cut off. We're still piecing it together, but it seems like a bioware experiment went wrong. We got eyes in the sky , but couldn't do any astral check out without being exposed. From what we saw, a local response team was sent in- about 15 minutes later they came back out firing and dragging four wounded or dead with them. An unidentified metahuman looking heat source chased them out, but they brought it down in a hail of fire. They immediately retreated, and there are probably only four to six hours before they are reinforced with regional forces. We'll provide more details if you'll accept, but the basics are we need you to get to that facility, extract our informant and any scientists you can, as well as some data. It's a fluid and developing situation, and you'll have significant information support - just don't expect anything direct, we're already too exposed as it is. We'll give you more details if you accept; the paycheck is (SUFFICIENTLY LARGE NUMBER) with some bonus clauses we can discuss after you accept. You can back out now to no hard feelings - continuing the conversation beyond this point puts us in a relationship where we understand you to be prospectively in our employ with all the usual implications. I'll give you fifteen minutes to talk it over with your team."
Now you've got it all:
A) Secret facility with unknown but vaguely biological experimentation.
B) A containment team due to arrive in 4-6 hours..or earlier. Estimates are, after all, just estimates.
C) A penetration into said facility to find survivors or not-survivors as you see fit, and a reliable reason to force them deeper into the lair...that paydata isn't on the entry level secretary's link after all.
D) The corp has obviously put informants into this rival facility. They equally obviously were willing to enter it's airspace with a drone and try an astral probe despite some exposure risk. Suffice to say they likely care a good deal about possessing this data and making sure it is not open everyone. They might not care if random trids of the Experiments disgrace Corp B, but they also don't need any stories about how three scientists that caused those experiments were quietly taken and delivered to someone else. If you really need to have the runners betrayed, there's your motive.
Then again, you could also say a serious runner team - AKA the type of people you send into unknown situations in secret facilities - are probably smart enough to know that data exclusivity is part of the deal, they are working for someone big, and that this is pretty obviously not a "lets drop this on the trix and see how long it takes for our employer to figure out there are only a few potential sources of that leak - including the X people they have in custody who probably didn't do it" and get away with it situation. That sort of behavior ends with midnight flashbangs and waking up in extrajudicial territory.
E) A tailorable situation GM side. An outside corp only knows as much as you want the runners to know. You can tailor the details to your vision for the level of exploration. Just remember the line from Ronin about not having enough info: "The price has gotta go up."
