Kaelen moves to search the bodies as well.

Investigation: 20 with Asariel's help

Asariel was not expecting to find anyone alive. He was hoping to find some information about who these people were so he will help Kaelen. 

The pair are heavily tattooed, aside from faces and hands, both are shaved bald, with tattoos over their head as well, but there were wearing wigs and long sleeves ton hide the tattoos.

The mud makes it easy to see their trail was coming from the keep.

The man was armed with a short sword and dagger, the woman, only a dagger, and she had a pouch with what appears to be various spell components,

They had a pouch heavy with gold and platinum, (40 platinum, 140 gold) and another with 3 potions, one blue, two red, and a scroll case. A second blue potion has fallen to the ground.

Do you open the scroll case?

Kaelen reports his findings to the others and collects the potions and coin to divide later. He will hand the scroll case to Mathias or Asariel, not having any use for it himself.

Asariel will most definitely open the scroll case (even if the way you worded that makes me think as a player this might be a bad idea) 

You find several papers in the scroll case.

Most are a manifest of goods one might need to run a civilized outpost self-sufficiently. not really any weapons, and one sheet is a listing of strange items and substances that you would assume to be components for spells or rituals.

The one separate is a letter. Written in a very fine hand, but using very simple common words, as if the writer didn't trust the intended recipients intelligence, the letter is addressed to Clan Leader Bollix of the Coldtooth Clan, from simply "Mazzek" signed with a sharp and pointy looking sigil.

The letter details a request, partly quoted here, "as per our agreement" to "obtain goods on my behalf and have your goblins deliver them to the keep." "I understand some of the dragonfolk have a quarrel with you, but they will not trouble you as they are guests in MY keep."

"'Mazzek'. Perhaps he was that voice we heard then," Kaelen remarks after Mathias relays the information, "We shouldn't stay here too long. I imagine Arista will want to hear this as well."

"Agreed. Let's get back to the cave." Mathias says. 

Not wishing to waste any supplies, Brekka gathers up the weapons the two dead souls had left behind before he agrees to head back to the cave.

Arista paces the mud-slick threshold until the party splashes back through the rain. As their report spills out, she listens in stiff silence, then taps her staff against her shield. “So—lizardfolk up top, a tattooed cult below, and goblins hauling supplies for someone calling himself Mazzek. That’s three factions dug in, and they’re planning for a long stay.” She glances northeast, toward the unseen walls. “We’ve got proof the keep is occupied and by whom. I say tomorrow we creep close enough for a good sketch of the defenses, then pull back to Threshold with our findings. A straight assault would be folly till the Duke knows what he’s facing.”

Asariel nods. "And we would be stupid to assume there are not more hidden defences inside. Or magical ones outside. We have triggered one magical trap already."

Kaelen nods as he sets out the potions for them to taste and identify, dividing up the coins equally as well. "Agreed. Curious as I am to head inside and meet this Mazzek, we do have a job to do."

((That's 8 platinum and 28 gold each I think))

If you take a short rest, you can identify the potions as two potions of gaseous form and two potions of healing.

Brekka is obviously restless at thought of simply looking at this fort. He frowns with disappointment.

"A look before reporting back," he agrees, "but next time we come back, we're going in!" he insists eagerly.

Arista fingers the vials, murmuring that she can sort their magic quickly if the rest insist on a breather—but she’d rather push on. “I say we hide the wagon here, post Torban with the mules, and head for the keep tonight,” she says, jerking her chin toward the cave’s deeper shadows. “Kaelen can rig an alarm spell at the entrance—still works if we’re within a mile—so we’ll know if trouble finds him. We watch the walls under cover of dark, take another look at dawn, then fall back to report. Thoughts?”

Asariel looks around. "I am all for that plan, however we do have to consider that not all of us can see in the dark. I can create light for the humans but I would advise against that for a reconnaissance mission. Stealth is of the upmost importance." He thinks for a minute. "We might be lucky and the keep might be lit so everyone can see the walls clearly."

Arista rubs a thumb along the rim of her shield, conceding the point with a nod. “You’re right—if the walls stay dark, I’ll be blind and a beacon if I carry light.” She glances to Kaelen, Brekka, Asariel, and Mathias in turn. “All of you can see in the night, and Mathias has other eyes if he needs them. I’ll stay here with Torban and the cart, keep the cave secure, and listen for Kaelen’s alarm. You four slip up, mark guard posts and gates, then circle back shortly after dawn. Ok?”

"We could do an initial check tonight, but even our sight has its limits in the dark. We can't see beyond the throw of a spear or two," Brekka rumbles.

((Is it still storming? Any lightning we could use to help see?))

Talking of a beacon gives Asariel an idea, though he isn't sure if they can execute it. But you don't know if you don't ask. "This might not be possible, but the angel blood in my veins allows me to light objects up. If I was to light up a small pebble or similar and we cover it up inside a pouch or other barrier, do people think we could launch it towards the keep and then have it emerge from it's cover? That way we can test the guards response to a threat when a beacon does appear, but they won't know what direction it came from to trace back to us."